1. Field of the Invention
The present invention relates to a recording method for recording audio and video information to an optical disk or similar optical information recording medium using a semiconductor laser (laser diode), and to the optical information recording medium itself.
2. Description of the Prior Art
The technologies needed to record and playback high density data to an optical disk or similar optical information recording medium using optical beam energy are well known, and a variety of devices that can be used to record audio and video information, also known as multimedia information, to optical disks are commercially available. An example of a conventional recording method for capturing multimedia information to an optical disk is described below with reference to FIGS. 11 and 12.
FIG. 11 shows a typical optical disk used in the conventional multimedia information recording method. Disk address information is recorded using lands and pits imprinted to the address areas 114, 115 of the disk, and the data is recorded to and read from the spiral data track 116 by means of scanning the track with an optical spot.
By driving the optical disk in FIG. 11 at 1800 rpm, a single NTSC-format image frame can be recorded in one revolution of the disk. More specifically, the first field is recorded to the first half revolution of the track 116 (A), and the second field is recorded to the other half revolution of the track 116 (B).
The upper part (a) of FIG. 12 shows a recording format used in this conventional multimedia information recording method.
An LPC (laser power control) area 117 is provided after the address 101 to set the laser power to a desired level in the first field, and is followed by area A1 118 for recording the first audio channel, a gap 119, area A2 120 for recording the second audio channel, a gap 121, video area 122 for recording the video information, a gap 123, area A3 124 for recording the third audio channel, a gap 125, and area A4 126 for recording the fourth audio channel.
The second field is recorded with a similar sequence: LPC field 129 following the address 128 to set the laser power to a desired level, area A1 130 for recording the first audio channel, a gap 131, area A2 132 for recording the second audio channel, a gap 133, video area 134 for recording the video information, a gap 135, area A3 136 for recording the third audio channel, a gap 137, and area A4 138 for recording the fourth audio channel.
The two LPC areas 117 and 129 are needed because the optical power must be set to an optimum power level for recording to an optical disk. A semiconductor laser is a current-driven device, and the optical output is controlled by adjusting the driving current. The driving current required to obtain a given optical output level, however, has a high temperature dependency. As a result, maintaining a constant driving current will not necessarily assure a constant optical output power. To obtain the optimum recording power, it is therefore necessary to monitor the optical output, regulate the driving current to control the optical output as required to obtain the required recording power, and thus adaptively set the driving current according to the optimum recording power. A predetermined time period is required to complete this operation, and the LPC areas 117 and 129 provide this period.
While the above description relates specifically to a semiconductor laser, the optical output of other light sources is also affected to varying degrees by the ambient temperature, and need for the LPC areas 117 and 129 thus remains.
The middle part (b) of FIG. 12 shows the laser waveform when the above data format is recorded to a phase-change erasable recording medium. With a phase-change erasable recording medium, the optical output is modulated between the playback power level and two higher power levels, specifically, bias and peak power levels; the bias power is used for data erasing, and the peak power level for recording.
During the LPC area 117, the optical output is set from the playback power P.sub.R to the bias power P.sub.B and the peak power P.sub.P. The laser power is thereafter modulated between these levels according to the type of information (audio or video) being recorded.
Audio and video information recorded in this format can be used in various ways, one being to record only the audio portion to a previously recorded video segment. Sometimes referred to as "after-recording," this presents several problems in the conventional recording method as described above.
Consider the use of after-recording with the conventional recording format illustrated in FIG. 12 (a) . The laser power waveform used at this time is shown in the lower part (c) of FIG. 12.
During the LPC area 117 the laser output is increased from the playback power P.sub.R to the bias power P.sub.B and then the peak power P.sub.P (period C). The laser is then modulated to record the first and second audio channels (period D), but must be dropped to the playback power P.sub.R level (period E) during the video field 122 because the video data is not to be changed.
The third and fourth audio channels 124, 126 should then be recorded, but cannot because the laser power has already been dropped to the playback power P.sub.R level, and there is no LPC area in which the optical output can be set. As a result, the third and fourth audio channels 124,126 are not recorded (period F).
As is obvious, the problem with the conventional recording method using this recording format is that satisfactory audio after-recording is not possible.